内蒙古额济纳平原地下水氢氧稳定同位素和水化学特征及其演化规律

魏世博; 王哲; 李飞; 吴玺; 徐蓉桢

doi:10.12029/gc20230112

内蒙古额济纳平原地下水氢氧稳定同位素和水化学特征及其演化规律

Characteristics of hydrogen and oxygen stable isotopes and hydrochemistry in the groundwater of Ejina plain, Inner Mongolia and its hydrochemical evolution

摘要

摘要:
研究目的 为研究内蒙古额济纳平原地下水水化学特征及其演化规律，于2020年8月采集水样87组，氢氧同位素样品69组。
研究方法 综合运用数理统计、离子比例分析、水文地球化学模拟等方法，分析额济纳平原第四系地下水及北部白垩系地下水水文地球化学特征，探讨水文地球化学演化规律。
研究结果 结果表明：（1）该区地下水水化学类型以SO₄-Na型为主。地下水中阴离子以SO₄^2-为主，其次为Cl^-；阳离子以Na⁺为主，Ca²⁺与Mg²⁺浓度差异不大。（2）研究区地下水SO₄^2-、Cl^-、TDS、总硬度、Na⁺和Mg²⁺浓度具有第四系承压水＞第四系潜水＞白垩系承压水的特点。（3）第四系潜水离子组分主要受溶滤作用、混合作用控制，局部地区受蒸发作用影响显著；第四系承压水离子组分主要受溶滤作用和阳离子交换作用控制；平原北部白垩系承压水离子组分受溶滤作用及阳离子交换作用控制。研究区地下水中主要离子来自岩盐、碳酸岩盐和石膏的溶解。
结论沿地下水流向，第四系潜水离子浓度组分呈增加趋势，在额济纳平原内部第四系潜水和承压水中主要发生岩盐、白云石和石膏溶解、方解石沉淀以及正向阳离子交换作用；研究区东南部沙漠与平原交错带主要发生岩盐、白云石和石膏溶解、方解石沉淀以及反向阳离子交换；平原区北部白垩系承压水中主要发生岩盐、白云石和石膏溶解、方解石沉淀以及正向阳离子交换。

Abstract:
This paper is the result of mineral exploration engineering.
Objective In order to study the hydrochemical characteristics and evolution of groundwater in the Ejina plain, Inner Mongolia, 87 water quality samples and 69 hydrogen and oxygen isotope samples were collected in August 2020.
Methods Based on the methods of mathematical statistics, ion ratio, and hydrogeochemical simulation, the hydrogeochemical characteristics and the hydrochemical evolution rule of groundwater stored in Quaternary aquifer and Cretaceous aquifer were analyzed.
Results The results showed that: (1) The groundwater was mainly SO₄-Na type. SO₄^2- was the main anion, followed by Cl^-. Na⁺ was the main cation, followed by Ca²⁺ and Mg²⁺, there was little difference between Ca²⁺ and Mg²⁺ concentrations. (2) The concentrations of SO₄^2-, Cl^-, TDS, total hardness, Na+ and Mg²⁺ decreased in the order of Quaternary confined water> Quaternary phreatic water> Cretaceous confined water. (3) Quaternary phreatic ions were mainly controlled by leaching and mixing process, and some areas were significantly affected by evaporation. The ions of Quaternary confined water were mainly controlled by leaching and cation exchange. The ions of the Cretaceous confined water in the northern part of the plain were controlled by leaching and cation exchange. The main ions of groundwater in the study area came from the dissolution of halite, carbonates and gypsum.
Conclusions Along the direction of groundwater flow, the concentration of ion components in Quaternary phreatic showed an increasing trend. In the Quaternary phreatic and confined water in the Ejina plain, the main water- rock interaction processes were dissolution of halite, dolomite and gypsum, precipitation of calcite, and positive cation exchange. In the interlaced zone between the desert and the plain in the southeast of the study area, the dissolution of halite, dolomite and gypsum, the precipitation of calcite, and reverse cation exchange mainly occurred. Halite, dolomite and gypsum dissolution, calcite precipitation, and positive cation exchange mainly occurred in the Cretaceous confined water in the northern plain.

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